This Program Project consists of eight individual projects. There are three universities (Duke University, California Institute of Technology - JPL, and University of California, Irvine) that will be collaborating with UCLA. There are 17 investigators (principal, co-investigators, or collaborators) from 12 laboratories organized to study the plasticity of the mammalian nervous and musculo-skeletal systems in response to neural lesions. Basically, three types of lesions will be used as models with the greatest concentration of effort on complete low thoracic spinal transection. Other models to be used include cerebellar plus spinal lesions, dorsal column lesions and hindlimb immobilization plus a spinal lesion. These studies are designed to ascertain the potential of the mammalian spinal cord and the experimental hindlimbs distal to the lesions of low thoracic, completely spinalized animals to recover motor functions after a lesion. By utilizing the potential for motor control that exists in lumbar pattern generators, the low thoracic, spinalized cats will be exercised on a treadmill for six months to promote functional recovery and maintenance of the hind limbs. This model provides a new and physiologically significant means of studying the specific mechanisms involved in the plasticity of the spinal cord and the neural control of protein synthesis of muscles in response to known levels of "use and disuse".